1. Field of the Invention
The present invention relates to stable well cementing methods and compositions, and more particularly, to such methods and well cement compositions which are thermally stable and degradation resistant.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in oil, gas and water well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a string of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened, substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the pipe to the walls of the well, bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
When conventional cement compositions are utilized for sealing pipe strings in well bores or for carrying out other remedial or repair procedures in high temperature wells including geothermal wells, the conventional cement compositions are unstable after setting due to settling of the particulate solids in the cement composition and suffer from strength degradation due to exposure to the high temperatures, corrosion and the like.
Thus, there are needs for improved cementing methods and compositions which are thermally stable and degradation resistant.
The present invention provides improved methods of sealing subterranean zones penetrated by well bores and improved thermally stable and degradation resistant well cement compositions which meet the above described needs and overcome the deficiencies of the prior art. The methods of the present invention basically comprise the following steps. An improved thermally stable and degradation resistant cement composition is provided comprised of a hydraulic cement, sufficient water to form a pumpable slurry, an aqueous hydrogenated styrene-butadiene rubber latex and a latex stabilizer present in an amount sufficient to stabilize the hydrogenated styrene-butadiene latex. The cement composition is placed in a subterranean zone to be cemented and thereafter, the cement composition is allowed to set into a hard, impermeable, thermally stable and degradation resistant mass.
The improved thermally stable and degradation resistant well cement compositions of this invention are basically comprised of a hydraulic cement, sufficient water to form a pumpable slurry, an aqueous hydrogenated styrene-butadiene rubber latex and a latex stabilizer present in an amount sufficient to stabilize the hydrogenated styrene-butadiene latex.
The hydrogenated styrene-butadiene rubber utilized in the aqueous latex thereof has in the range of from about 80% to about 95% of the available carbon valence bonds attached to separate other atoms. The weight ratio of styrene to butadiene in the hydrogenated styrene-butadiene rubber is in the range of from about 5:95 to about 95:5. The presence of the hydrogenated styrene-butadiene rubber in the cement composition provides improved thermal stability at high temperatures as well as improved strength and corrosion degradation resistance at high temperatures.
The objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.